The Moon is the only natural satellite of the Earth, Consider as a fifth largest satellite in the Solar System. It is the largest natural satellite in the Solar System relative to the size of its planet, a quarter the diameter of Earth and 1/81 its mass, and is the second densest satellite after Io. It is in synchronous rotation with Earth, always showing the same face. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal.

The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses.

The Moon is the only celestial body on which humans have landed, And the Soviet Union was the first to reach the Moon with unmanned spacecraft in 1959, the try followed by the United States adventure to achieve the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972—the first being Apollo 11 in 1969. These missions returned over 380 kg of lunar rocks, which have been used to develop a detailed geological understanding of the Moon's origins.

The prevailing hypothesis today is that the Earth–Moon system formed as a result of a giant impact: a Mars-sized body hit the nearly formed proto-Earth, blasting material into orbit around the proto-Earth, which accreted to form the Moon.Giant impacts are thought to have been common in the early Solar System.